In order to save installation space in the cylinder head of a motor vehicle, there is a trend toward long, slender spark plugs. For this purpose, the wall thicknesses of the ceramic insulator, in particular in the root area of the spark plugs determining the geometry of the center electrodes, are also decreased. This frequently results in problems with the electrical strength, particularly in combustion chamber-side areas in which additionally the cross section of the insulator is reduced, since very high field strengths are present here. The service life of such spark plugs having a reduced installation space is thus low.